U.S. patent number 6,249,598 [Application Number 08/968,125] was granted by the patent office on 2001-06-19 for solder testing apparatus.
This patent grant is currently assigned to Hitachi, Ltd., Siemens Aktiengesellshaft. Invention is credited to Guenter Doemens, Toshifumi Honda, Ludwig Listl, Yukio Matsuyama, Peter Mengel.
United States Patent |
6,249,598 |
Honda , et al. |
June 19, 2001 |
Solder testing apparatus
Abstract
A solder testing apparatus comprising image processing means for
performing image processing on an image of an appearance of a
soldered portion to identify shape characterizing amounts for the
soldered portion; and defect determining means for performing
good/bad determination on the soldered portion from data derived by
the image processing means and data from test parameter storing
means for storing shape characterizing amounts at design time,
wherein tested-object standard shape estimating means is included
for extracting shape characterizing amounts of a non-defective
soldered portion by statistically processing shape characterizing
amounts for soldered portions identified by the image processing
means, and defect determining parameters stored in the test
parameter storing means are updated based on standard shape values
from the tested-object standard shape estimating means, so that a
highly reliable test is realized by setting defect determining
parameters based on actual shapes and dimensions of leads and pads
of electronic components on a printed circuit board.
Inventors: |
Honda; Toshifumi (Funabashi,
JP), Matsuyama; Yukio (Tochigi-ken, JP),
Doemens; Guenter (Holzkirchen, DE), Mengel; Peter
(Eichenau, DE), Listl; Ludwig (Munich,
DE) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
Siemens Aktiengesellshaft (Munich, DE)
|
Family
ID: |
17885155 |
Appl.
No.: |
08/968,125 |
Filed: |
November 12, 1997 |
Foreign Application Priority Data
|
|
|
|
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Nov 12, 1996 [JP] |
|
|
8-300467 |
|
Current U.S.
Class: |
382/150; 382/146;
250/559.34 |
Current CPC
Class: |
G01R
31/71 (20200101); G01R 31/309 (20130101) |
Current International
Class: |
G01R
31/28 (20060101); G01R 31/309 (20060101); G01R
31/04 (20060101); G01R 31/02 (20060101); G06K
009/00 () |
Field of
Search: |
;382/146-150,154,170
;348/87,126 ;702/82,152,34 ;356/375,376,384,394,237.4,237.5
;700/110,121 ;250/559.2,559.27,559.34,559.46 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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41 39 189 A1 |
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Nov 1992 |
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DE |
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0 195 161 A1 |
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Sep 1986 |
|
EP |
|
0 685 732 A1 |
|
Dec 1995 |
|
EP |
|
62-261148 |
|
Nov 1987 |
|
JP |
|
8-193816 |
|
Jul 1996 |
|
JP |
|
8-327559 |
|
Dec 1996 |
|
JP |
|
Other References
Electronic Packaging Technology, vol. 9, No. 2, pp. 67-71 and
English translation thereof..
|
Primary Examiner: Boudreau; Leo
Assistant Examiner: Werner; Brian P.
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus, LLP
Claims
What is claimed is:
1. A solder testing apparatus comprising image detecting means for
detecting an appearance image of a soldered portion of an
electronic component under testing mounted by soldering leads of
the electronic component to pads on a printed circuit board; image
processing means for performing image processing on said appearance
image to identify shape characterizing amounts of said soldered
portion; test parameter storing means for storing image processing
parameters used in said image processing means and defect
determining parameters used for determining whether said soldered
portion is good or bad; and defect determining means for
determining whether said soldered portion is good or bad from data
derived from said image processing means and the defect determining
parameters stored in said test parameter storing means;
wherein said image processing means calculates shape factors of a
lead and a pad for each soldered portion as shape characterizing
amounts for the soldered portion, and
said solder testing apparatus further comprising:
tested-object shape accumulating means for storing shape
characterizing amounts of soldered portions identified by said
image processing means;
tested-object standard shape estimating means for identifying
design shape factors of leads and pads as standard shape
characterizing amounts, and extracting said standard shape
characterizing amounts from the accumulated shape characterizing
amounts for soldered portions, based on the shape characterizing
amounts for soldered portions stored in said tested-object shape
accumulating means; and
test parameter updating means for updating the image processing
parameters and the defect determining parameters stored in said
test parameter storing means based on said standard shape
characterizing amounts;
wherein said image processing means identifies, for each soldered
portion, shape factors of a solder fillet, together with the shape
factors of a lead and a pad, as shape characterizing amounts for
the soldered portion; and
wherein said tested-object standard shape estimating means
statistically processes the shape characterizing amounts for the
soldered portions stored in said tested-object shape accumulating
means for each type of electronic component mounted on the printed
circuit board to identify, from said accumulated shape
characterizing amounts for the soldered portions, shape
characterizing amounts corresponding to shape factors of leads and
pads and shape factors of defective solder fillets which exhibit a
low detecting frequency or which cannot be normally derived
theoretically from a structural viewpoint, as unnecessary shape
characterizing amounts, and to identify shape characterizing
amounts corresponding to shape factors of leads and pads an shape
factors of non-defective solder fillets which exhibit a high
detecting frequency as standard shape characterizing amounts, and
extracts said standard shape characterizing amounts from said
accumulated shape characterizing amount for the soldered
portions.
2. A solder testing apparatus according to claim 1, wherein said
shape factors of solder fillets in said image-processing means
comprise at least one of a height of a fillet, a width of the
fillet, an area of the fillet in contact with a lead, a length of
the fillet, a volume of the fillet, and a wet angle at a portion at
which the fillet is in contact with the lead.
3. A solder testing apparatus according to claim 2, wherein said
defect determining means performs good/bad determination in
combination of said fillet height and said wet angle at a portion
at which a fillet is in contact with a lead, and determines as
defective if said fillet height derived from said appearance image
is lower than a threshold value set in correspondence to said
fillet height, and if said wet angle derived from said appearance
image is smaller than a threshold value set in correspondence to
said wet angle.
4. A solder testing apparatus, comprising image detecting means for
detecting an appearance image of a soldered portion of an
electronic component under testing mounted by soldering leads of
the electronic component to pads on a printed circuit board; image
processing means for performing image processing on said appearance
image to identify shape characterizing amounts of said soldered
portion; test parameter storing means for storing image processing
parameters used in said image processing means and defect
determining parameters used for determining whether said soldered
portion is good or bad; and defect determining means for
determining whether said soldered portion is food or bad from data
derived from said image processing means and the defect determining
parameters stored in said test parameter storing means;
wherein said image processing means calculates shape factors of a
lead and a pad for each soldered portion as shape characterizing
amounts for the soldered portion, and
said solder testing apparatus further comprising:
tested-object shape accumulating means for storing shape
characterizing amounts of soldered portions identified by said
image processing means;
tested-object standard shape estimating means for identifying
design shape factors of leads and pads as standard shape
characterizing amounts, and extracting said standard shape
characterizing amounts from the accumulated shape characterizing
amounts for soldered portions, based on the shape characterizing
amounts for soldered portions stored in said tested-object shape
accumulating means; and
test parameter updating means for updating the image processing
parameters and the defect determining parameters stored in said
test parameter storing means based on said standard shape
characterizing amounts;
wherein the image processing parameters and the defect determining
parameters updated by said test parameter updating means are
recorded in a storage unit at predetermined time intervals together
with model numbers of electronic components, date and time.
5. A solder testing apparatus according to claim 4, wherein said
image processing parameters and said defect determining parameters
recorded at predetermined time intervals are automatically
preserved as backup when they have been recorded a predetermined
number of times.
6. A solder testing apparatus comprising image detecting means for
detecting an appearance image of a soldered portion of an
electronic component under testing mounted by soldering leads of
the electronic component to pads on a printed circuit board; image
processing means for performing image processing on said appearance
image to identify shape characterizing amounts of said soldered
portion; test parameter storing means for storing image processing
parameters used in said image processing means and defect
determining parameters used for determining whether said soldered
portion is good or bad; and defect determining means for
determining whether said soldered portion is good or bad from data
derived from said image processing means and the defect determining
parameters stored in said test parameter storing means;
wherein said image Processing means calculates shape factors of a
lead and a pad for each soldered portion as shape characterizing
amounts for the soldered portion; and
said solder testing apparatus further comprising:
tested-object shape accumulating means for storing shape
characterizing amounts of soldered portions identified by said
image processing means;
tested-object standard shape estimating means for identifying
design shape factors of leads and pads as standard shape
characterizing amounts, and extracting said standard shape
characterizing amounts from the accumulated shape characterizing
amounts for soldered portions, based on the shape characterizing
amounts for soldered portions stored in said tested-object shape
accumulating means; and
test parameter updating means for updating the image processing
parameters and the defect determining parameters stored in said
test parameter storing means based on said standard shape
characterizing amounts;
wherein said tested-object standard shape estimating means
approximates the shape characterizing amounts accumulated in said
tested-object shape accumulating means with a first-order straight
line; and
wherein said defect determining means determines whether a soldered
portion is good or bad by comparing a shape characterizing amount
of the soldered portion derived from said image processing means
with said first-order straight line.
7. A solder testing apparatus comprising image detecting means for
detecting an appearance image of a soldered portion of an
electronic component under testing mounted by soldering leads of
the electronic component to pads on a printed circuit board; image
processing means for performing image processing on said appearance
image to identify shape characterizing amounts of said soldered
portion; test parameter storing means for storing image processing
parameters used in said image processing means and defect
determining parameters used for determining whether said soldered
portion is good or bad; and defect determining means for
determining whether said soldered portion is good or bad from data
derived from said image processing means and the defect determining
parameters stored in said test parameter storing means;
wherein said image processing means calculates shape factors of a
lead and a pad for each soldered portion as shape characterizing
amounts for the soldered portion; and
said solder testing apparatus further comprising:
tested-object shape accumulating means for storing shape
characterizing amounts of soldered portions identified by said
image processing means;
tested-object standard shape estimating means for identifying
design shape factors of leads and pads as standard shape
characterizing amounts, and extracting said standard shape
characterizing amounts from the accumulated shape characterizing
amounts for soldered portions, based on the shape characterizing
amounts for soldered portions stored in said tested-object shape
accumulating means; and
test parameter updating means for updating the image processing
parameters and the defect determining parameters stored in said
test parameter storing means based on said standard shape
characterizing amounts;
wherein said image detecting means is capable of detecting a
surface height image of said object under testing;
wherein said image processing means detects a height of a top
surface of a lead and a height of a surface of a pad from said
surface height image;
wherein said tested-object shape accumulating means accumulates a
value derived by subtracting the pad surface height from the lead
top surface height as a lead thickness; and
wherein said tested-object standard shape estimating means
estimates that a peak for the smallest lead thickness indicates an
actual lead thickness within peaks in a histogram for lead
thicknesses accumulated in said tested-object shape accumulating
means.
8. A solder testing apparatus comprising image detecting means for
detecting an appearance image of a soldered portion of an
electronic component under testing mounted by soldering leads of
the electronic component to pads on a printed circuit board; image
processing means for performing image processing on said appearance
image to identify shape characterizing amounts of said soldered
portion; test parameter storing means for storing image processing
parameters used in said image processing means and defect
determining parameters used for determining whether said soldered
portion is good or bad; and defect determining means for
determining whether said soldered portion is good or bad from data
derived from said image processing means and the defect determining
Parameters stored in said test parameter storing means;
wherein said image processing means calculates shape factors of a
lead and a pad for each soldered portion as shape characterizing
amounts for the soldered portion, and
said solder testing apparatus further compressing:
tested-object shape accumulating means for storing shape
characterizing amounts of soldered portions identified by said
image processing means;
tested-object standard shape estimating means for identifying
design shape factors of leads and pads as standard shape
characterizing amounts, and extracting said standard shape
characterizing amounts from the accumulated shape characterizing
amounts for soldered portions, based on the shape characterizing
amounts for soldered portions stored in said tested-object shape
accumulating means; and
test parameter updating means for updating the image processing
parameters and the defect determining parameters stored in said
test parameter storing means based on said standard shape
characterizing amounts;
wherein said image detecting means is capable of detecting a
brightness image of said object under testing;
wherein said image processing means detects a lead width from said
brightness image;
wherein said tested-object shape accumulating means accumulates
said lead width; and
wherein said tested-object standard shape estimating means
estimates that the narrowest peak indicates an actual lead width
within peaks in a histogram for lead widths stored in said
tested-object shape accumulating means.
9. A solder testing apparatus comprising image detecting means for
detecting an appearance image of a soldered portion of an
electronic component under testing mounted by soldering leads of
the electronic component to Dads on a printed circuit board; image
processing means for performing image processing on said appearance
image to identify shape characterizing amounts of said soldered
portion; test parameter storing means for storing image processing
parameters used in said image processing means and defect
determining parameters used for determining whether said soldered
portion is good or bad; and defect determining means for
determining whether said soldered portion is good or bad from data
derived from said image processing means and the defect determining
parameters stored in said test parameter storing means;
wherein said image processing means calculates shape factors of a
lead and a pad for each soldered portion as shape characterizing
amounts for the soldered portion, and
said solder testing apparatus further comprising:
tested-object shape accumulating means for storing shape
characterizing amounts of soldered portions identified by said
image processing means;
tested-object standard shape estimating means for identifying
design shape factors of leads and pads as standard shape
characterizing amounts, and extracting said standard shape
characterizing amounts from the accumulated shape characterizing
amounts for soldered portions, based on the shape characterizing
amounts for soldered portions stored in said tested-object shape
accumulating means; and
test parameter updating means for updating the image processing
parameters and the defect determining parameters stored in said
test parameter storing means based on said standard shape
characterizing amounts;
wherein said test parameter storing means stores shape factors of
leads and pads at design time, inputted by a user; and
wherein said tested-object standard shape estimating means compares
said shape factors inputted by the user with shape characterizing
amounts for a nondefective soldered portion estimated based on
shape characterizing amounts stored in said tested-object shape
accumulating means, determines that an erroneous estimation has
been made if a difference derived from the comparison is larger
than a set threshold value, and does not update the test
parameters.
10. A solder testing apparatus comprising image detecting means for
detecting an appearance image of a soldered portion of an
electronic component under testing mounted by soldering leads of
the electronic component to pads on a printed circuit board; image
processing means for performing image processing on said appearance
image to identify shape characterizing amounts of said soldered
portion; test parameter storing means for storing image processing
parameters used in said image processing means and defect
determining parameters used for determining whether said soldered
portion is good or bad; and defect determining means for
determining whether said soldered portion is good or bad from data
derived from said image processing means and the defect determining
parameters stored in said test parameter storing means,
wherein said image processing means calculates shape factors of a
lead and a pad for each soldered portion as shape characterizing
amounts for the soldered portion, and
said solder testing apparatus further comprising:
tested-object shape accumulating means for storing shape
characterizing amounts of soldered portions identified by said
image processing means;
tested-object standard shape estimating means for statistically
processing the shape characterizing amounts for soldered portions,
accumulated in said tested-object shape accumulating means for each
type of electronic component mounted on the printed circuit board,
to identify, from said stored shape characterizing amounts for
soldered portions, shape factors of leads and pads which exhibit a
low detecting frequency or which cannot be normally derived
theoretically from a structural viewpoint, as unnecessary shape
characterizing amounts, and to identify shape factors of leads and
pads which exhibit a high detecting frequency as standard shape
characterizing amounts, and for extracting said standard shape
characterizing amounts from said accumulated shape characterizing
amount for the soldered portions; and
test parameter updating means for updating the image processing
parameters and the defect determining parameters stored in said
test parameter storing means based on said standard shape
characterizing amounts.
11. A solder testing apparatus according to claim 10,
wherein said image processing means identifies, for each soldered
portion, shape factors of a solder fillet, together with the shape
factors of a lead and a pad, as shape characterizing amounts for
the soldered portion; and
wherein said tested-object standard shape estimating means
statistically processes the shape characterizing amounts for the
soldered portions stored in said tested-object shape accumulating
means for each model to identify, from said accumulated shape
characterizing amounts for the soldered portions, shape
characterizing amounts corresponding to shape factors of leads and
pads and shape factors of defective solder fillets which exhibit a
low detecting frequency or which cannot be normally derived
theoretically from a structural viewpoint, as unnecessary shape
characterizing amounts, and to identify shape characterizing
amounts corresponding to shape factors of leads and pads and shape
factors of non-defective solder fillets which exhibit a high
detecting frequency as standard shape characterizing amounts, and
extracts said standard shape characterizing amounts from said
accumulated shape characterizing amount for the soldered
portions.
12. A solder testing apparatus according to claim 11, wherein said
shape factors of solder fillets in said image processing means
comprise at least one of a height of a fillet, a width of the
fillet, an area of the fillet in contact with a lead, a length of
the fillet, a volume of the fillet, and a wet angle at a portion at
which the fillet is in contact with the lead.
13. A solder testing apparatus according to claim 12, wherein said
defect determining means performs good/bad determination in
combination of said fillet height and said wet angle at a portion
at which a fillet is in contact with a lead, and determines as
defective if said fillet height derived from said appearance image
is lower than a threshold value set in correspondence to said
fillet height, and if said wet angle derived from said appearance
image is smaller than a threshold value set in correspondence to
said wet angle.
14. A solder testing apparatus according to claim 10, wherein said
tested-object standard shape estimating means extracts shape
characterizing amounts for a non-defective unit based on shape
characterizing amounts of soldered portions from an appropriate
number of printed circuit boards for each type of lead.
15. A solder testing apparatus according to claim 10, wherein the
image processing parameters and the defect determining parameters
updated by said test parameter updating means are recorded in a
storage unit at predetermined time intervals together with model
numbers of electronic components, date and time.
16. A solder testing apparatus according to claim 15, wherein said
image processing parameters and said defect determining parameters
recorded at predetermined time intervals are automatically
preserved as backup when they have been recorded a predetermined
number of times.
17. A solder testing apparatus according to claim 16, wherein said
tested-object standard shape estimating means derives a histogram
for or a mean value of shape characterizing amounts accumulated in
said tested-object shape accumulating means for each type of lead
or for each of groups when the leads are divided into the groups,
and extracts said standard shape characterizing amounts based on a
peak position of said histogram or said mean value.
18. A solder testing apparatus according to claim 10,
wherein said tested-object standard shape estimating means
approximates the shape characterizing amounts accumulated in said
tested-object shape accumulating means with a first-order straight
line; and
wherein said defect determining means determines whether a soldered
portion is good or bad by comparing a shape characterizing amount
of the soldered portion derived from said image processing means
with said first-order straight line.
19. A solder testing apparatus according to claim 10,
wherein said image detecting means is capable of detecting a
surface height image of said object under testing;
wherein said image processing means detects a height of a top
surface of a lead and a height of a surface of a pad from said
surface height image;
wherein said tested-object shape accumulating means accumulates a
value derived by subtracting the pad surface height from the lead
top surface height as a lead thickness; and
wherein said tested-object standard shape estimating means
estimates that a peak for the smallest lead thickness indicates an
actual lead thickness within peaks in a histogram for lead
thicknesses accumulated in said tested-object shape accumulating
means.
20. A solder testing apparatus according to claim 10,
wherein said image detecting means is capable of detecting a
brightness image of said object under testing;
wherein said image processing means detects a lead width from said
brightness image;
wherein said tested-object shape accumulating means accumulates
said lead width; and
wherein said tested-object standard shape estimating means
estimates that the narrowest peak indicates an actual lead width
within peaks in a histogram for lead widths stored in said
tested-object shape accumulating means.
21. A solder testing apparatus according to claim 10,
wherein said test parameter storing means stores shape factors of
leads and pads at design time, inputted by a user; and
wherein said tested-object standard shape estimating means compares
said shape factors inputted by the user with shape characterizing
amounts for a non-defective soldered portion estimated based on
shape characterizing amounts stored in said tested-object shape
accumulating means, determines that an erroneous estimation has
been made if a difference derived from the comparison is larger
than a set threshold value, and does not update the test
parameters.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for testing soldering
states of electronic components mounted on a printed circuit board,
and more particularly to a solder testing apparatus for use in a
manufacturing process where correct model numbers of electronic
components on printed circuit boards cannot be generally identified
due to the electronic components having the same electric
characteristics being supplied from a plurality of manufactures, or
the like.
As for an apparatus for testing soldering states of electronic
components mounted on printed circuit boards, there have been
failure detecting techniques, for example, as in a high speed
solder appearance testing apparatus SV2000 described in Electronic
Package Technology, Vol. 9, No. 2, 1993. Specifically, when
disturbance occurs, or when a new type of boards are tested for the
first time, several boards, appearing to be non-defective, are
extracted from a lot and applied to the apparatus to derive a mean
value and dispersion from their characterizing amounts, and a
failure is determined if the characterizing amounts detected from
an object under testing during a test deviate from the mean value
of the previously derived characterizing amounts of the
non-defective boards by a predetermined amount.
However, the above-mentioned prior art technique has difficulties
in supporting disturbance in a process and frequent changes of
parts mounted on boards during testing. Generally, even with
printed circuit boards under testing of the same type, electronic
components labelled with different model numbers, which have the
same electric characteristics but possibly slightly different
appearances, are often treated as the same components and mounted
on the boards. When a plurality of component manufacturers provide
electronic components having the same electric characteristics,
appearances of the electronic components manufactured by different
manufacturers, for example, a lead thickness, a lead width, and so
on may slightly differ from each other.
Generally, electronic components used to be mounted on printed
circuit boards are supplied from the most beneficial one of
manufacturers, which manufacture the components having the same
electric characteristics, in terms of the price, delivery time, and
so on, at the time the electronic components are to be supplied.
For this reason, components from different manufacturers may
possibly be mounted on printed circuit boards of the same type
depending on manufacturing periods. In the prior art, test data is
newly created from non-defective boards only when disturbance
occurs in a process during testing. Generally, however, information
on used electronic components and changes in processes is not
available in a testing step.
For this reason, conventionally, a plurality of components labelled
with different model numbers, having electrodes of slightly
different design dimensions, have been inevitably subjected to
testing using the same image processing parameters and defect
determining parameters. Also, while the prior art relies on a mean
value for determining a defect, it is difficult for this scheme to
conduct a test based on testing specifications used in
manufacturing sites. Generally, in manufacturing sites, the testing
specifications are generally determined in many cases based on the
shapes of leads and pads, for example, a failure is determined when
a lead deviates from a pad by three percents or more of the width
of the lead. However, since the prior art does not obtain these
shapes from images, a highly reliable test cannot be realized.
SUMMARY OF THE INVENTION
It is an object of the present invention to realize a highly
reliable test by setting image processing parameters and failure
determining parameters based on actual shapes and dimensions of
electrode portions (leads) and pads of electronic components
mounted on printed circuit boards under testing.
The above object is realized by the following configuration.
A solder testing apparatus comprising image detecting means for
detecting an appearance image of a soldered portion of an
electronic component under testing mounted by soldering leads of
the electronic component to pads on a printed circuit board, image
processing means for performing image processing on the appearance
image to identify shape characterizing amounts of the soldered
portion, test parameter storing means for storing image processing
parameters used in the image processing means and defect
determining parameters used for determining whether the soldered
portion is good or bad, and defect determining means for
determining whether the soldered portion is good or bad from data
derived from the image processing means and the defect determining
parameters stored in the test parameter storing means, wherein the
image processing means identifies shape factors of a lead and a pad
and/or a shape factor of a solder fillet for each soldered portion
as shape characterizing amounts for the soldered portion, and the
solder testing apparatus has tested-object shape accumulating means
for storing shape characterizing amounts of soldered portions
identified by the image processing means, tested-object standard
shape estimating means for statistically processing the shape
characterizing amounts for soldered portions, accumulated in the
tested-object shape accumulating means for each model, to identify,
from the stored shape characterizing amounts for soldered portions,
shape characterizing amounts corresponding to shape factors of
leads and pads and shape factors of defective solder. fillets which
exhibit a low detecting frequency or which cannot be normally
derived theoretically from a structural viewpoint, as unnecessary
shape characterizing amounts, and to identify shape characterizing
amounts corresponding to shape factors of leads and pads and/or
shape factors of non-defective solder fillets which exhibit a high
detecting frequency as standard shape characterizing amounts, and
for extracting the standard shape characterizing amounts from the
accumulated shape characterizing amount for the soldered portions,
and test parameter updating means for updating the image processing
parameters and the defect determining parameters stored in the test
parameter storing means based on the standard shape characterizing
amounts.
A detecting optical system provided in the solder testing apparatus
detects an image of a soldered portion under testing, and this
image is processed by the image processing means. The image
processing means detects shapes and dimensions of leads and pads of
electronic components from images, and accumulates the detection
results in the tested-object shape accumulating means. At the time
the detection has been terminated for a complete board or a
plurality of boards, a histogram for detected shapes is derived for
each type of lead or pad, and values presenting maximum frequencies
are determined to be standard shape characterizing amounts for
actual shapes of a lead or a pad and of a solder fillet.
The image processing parameters and the defect determining
parameters are updated in test data updating means based on the
above-mentioned standard shape characterizing amounts. Since test
data are constantly updated, irrespective of before the test or
during the test, based on standard shape characterizing amounts for
the shapes and dimensions of leads and pads and for solder fillets
derived from actually detected images, it is possible to conduct
the test using the most appropriate test data for components under
test even if model numbers of mounted components have been changed
in the middle while a plurality of boards of the same type are
being tested in succession.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic configuration diagram illustrating a main
portion of a first embodiment of a solder testing apparatus
according to the present invention.
FIG. 2 is an embodiment of a testing algorithm for the solder
testing apparatus according to the present invention.
FIG. 3 is an embodiment of a lead thickness detecting algorithm for
the solder testing apparatus according to the present
invention.
FIG. 4 is an embodiment of an algorithm for detecting a lead width
and a pad width for the solder testing apparatus according to the
present invention.
FIG. 5 is an embodiment of a testing sequence for the solder
testing apparatus according to the present invention.
FIG. 6 is an embodiment of a testing sequence for the solder
testing apparatus according to the present invention.
FIG. 7 is an embodiment of a testing sequence for the solder
testing apparatus according to the present invention.
FIG. 8 is an embodiment of a testing sequence for the solder
testing apparatus according to the present invention.
FIG. 9 is a schematic configuration diagram illustrating a main
portion of an embodiment of a solder testing apparatus according to
the present invention.
FIG. 10 is an embodiment of a testing algorithm for the solder
testing apparatus according to the present invention.
FIG. 11 is an example of a detected characterizing amount which is
detected from an object under testing of the solder testing
apparatus according to the present invention.
FIG. 12 is an example of correlation between a distribution of
lengths of solder fillets, detected by the solder testing apparatus
of the present invention, and a defect determining threshold
value.
FIG. 13 is an example of a defect determining method based on
heights of solder fillets detected by the solder testing apparatus
of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will hereinafter be described with reference
to FIGS. 1-13. Here, reference numeral 101 designates a printed
circuit board; 102 an electronic component under testing; 103 an XY
stage; 104 an image detector; 105 a slit light projector; 106 a
galvano mirror; 107 an image input means; 108 a light cutting line
extracting means; 109 a light cutting line accumulating means; 110
a test parameter storing means; 111 a image processing and
tested-object shape detecting means; 113 a defect determining
means; 114 a tested-object shape accumulating means; 115 a
tested-object design dimension estimating means; 116 a test
parameter updating means; 201, 301, 401 leads; 202, 302, 402 pads;
203, 403 solder fillets; and 204, 404 image processing windows,
respectively.
FIG. 1 illustrates an example of a general configuration of the
present invention. 101 designates the printed circuit board under
testing. 102 designates the electronic component mounted on the
printed circuit board. The printed circuit board is fixed on the XY
table 103. 104 designates the image detector. Since the XY table
103 is movable in X- or Y-direction, an image at any position on
the printed circuit board can be detected by the image detector
104.
105 designates the slit light projector, which is capable of
irradiating an object under testing through the galvanomirror 106.
Slit light irradiated to an object under testing is detected by the
image detector 104, and converted into a digital image in the image
input means 107. A two-dimensional image, after converted to a
digital image in 107, is converted into one-dimensional waveform
data indicative of a height at a slit light irradiating position in
the light cutting line extracting means 108. In other words, the
height of the object under testing can be derived by a known light
cutting method.
The foregoing processing is performed while scanning a slit light
irradiating position by changing the angle of the galvanomirror
106, to detect a large number of one-dimensional height waveform
data which are stored in the light cutting line accumulating means
109. Brightness of the slit light at each light cutting line
extracting position is also stored in 109 in combination. In the
image processing and tested-object shape detecting means 111, an
image processing window is set based on pad design position data
stored in the test parameter storing means 110, and image
processing is performed on each light cutting line within the image
processing window to detect the shape of the object under
testing.
More specifically, in FIG. 2, an image processing window 204 is set
for testing a soldered portion at the tip of a lead 201, and light
cutting lines A detected on the lead 201 within a light cutting
line waveform in 204 are digitized by a height threshold value
stored in the test parameter storing means 110 (which stores a lead
thickness, a lead width, a pad width of an object under testing
previously inputted by the user, and which stores and updates a
lead thickness, a lead width, and a pad width estimated by actual
measurements made to those of the object under testing). Edges of
the digitized waveform are determined to be side edges, and the
height of the top surface of the lead is derived based on a height
indicated by the light cutting lines between these edges. Next, the
height of the surface of a pad or the board is derived from light
cutting lines 207 detected on a pad portion 202.
Next, from light cutting lines 206 detected on the solder fillet
203, a light cutting line portion higher than the pad height
derived from the light cutting lines 207 is determined to be a
solder fillet. Also, data on brightness of the slit light at a
light cutting line extracting position 207 is projected in the
direction indicated in FIG. 2 to produce a projection waveform
illustrated in 208, and these edge positions are determined to be
side edges. These detection results are accumulated in the
tested-object shape accumulating means 114.
After the foregoing processing has been performed, a height shape
at a position to which no light cutting lines have been irradiated,
i.e., a height shape of the entire object under testing is
determined based on interpolation of heights indicated by the two
light cutting lines closest to that position, in the image
processing and tested-object shape detecting means 111.
Next, it is determined in the defect determining means 113 whether
or not an associated soldered portion is defective. Whether or not
the lead is lifted is determined by the height h1 of the top
surface of the lead and the height ph of the height of the pad
derived by the image processing and tested-object shape detecting
means 111. Assuming that a design thickness of the lead stored in
the test parameter storing means is designated "thick," a lift
amount "lift" of the lead from the pad is calculated as
follows:
When lift is equal to or more than a constant threshold value, the
lead is detected as lift failure. Also, a lead
misplacement"misplacement" is calculated as follows, based on the
side edges le of the lead and the side edge pe of the pad:
Here, the lead is detected as misplacement failure if the lead is
deviated from the pad toward the outside, and misplacement is equal
to or more than a constant ratio with respect to a design width 1w
of the lead stored in a test parameter.
As described above, since the lift failure and the misplacement
failure are determined using a design thickness and a design width
of a lead, provided as test parameters,accurate design thickness
and design width of the lead are essential for realizing a highly
reliable test. However, in actual electronic board mounting sites,
components having the same electric characteristics are generally
supplied from a plurality of manufacturers, and the components
having the same electric characteristics are treated completely the
same irrespective of the manufacturers of the components. However,
since these components often differ slightly from each other in
actual shape, it is difficult to have previously created test data
which describes accurate component dimensions.
Also, since the dimensions of leads, particularly lead thicknesses,
have a large error margin in design dimensions, it is difficult to
independently measure accurate dimensions for all components in the
working sites, even if component manufacturers can be identified.
For this reason, the present invention updates the test parameters
based on the detected shapes and dimensions of the electrodes
(leads) and the pads detected in the image processing and
tested-object shape detecting means 111.
The tested-object design dimension estimating means 115 estimates
the dimension of a component based on the shape of an object under
testing detected by the image processing and tested-object shape
detecting means 111. First, a method of estimating a lead thickness
will be described with reference to FIG. 3. When the detecting
optical system of FIG. 1 is employed, a height to be detected is
the height of the top surface 301 of the lead with reference to the
pad 302. 303 designates a normal lead; 304 a lead with lift
failure; and 305 a lead with misplacement failure.
A detected height is higher than the lead thickness in 304 because
lift has occurred, and is lower than the lead thickness in 305
because the lead slips off from the pad to cause misplacement. 306
illustrates a histogram of lead heights detected for components of
the same type mounted on all printed circuit boards. While the
occurrence of failures such as 304 or 305 causes a detected height
to be higher or lower than the lead thickness, it is generally
known that a failure occurring ratio in actual manufacturing sites
is at most 1% or less, so that the peak of the histogram 306
indicates the lead thickness. Alternatively, a mean value of lead
thicknesses may be used instead of the histogram of the peak.
When a manufacturing process for a printed circuit board is
modified, for example, by introducing a new reflow furnace, the
process is not stabilized so that it can be thought that a large
amount of failures will result, where a maximum peak is not
necessarily a lead thickness.
In this case, the misplacement failure detection is first
conducted, and a histogram is calculated only from lead heights of
leads, which are determined to be free from misplacement failure as
a result, and the lowest peak of peaks in the histogram is
designated as a normal lead thickness, thereby making it possible
to detect an accurate lead height. This is because, as illustrated
in FIG. 3, the height of a lead, slipped off a pad, is detected to
be lower than a lead thickness, while it is otherwise detected to
be equal to or higher than the lead thickness. Therefore, when a
histogram is calculated for lead heights of leads free from
misplacement failure, the lowest peak is equal to the lead
thickness.
A method of estimating a lead width will be described with
reference to FIG. 4. 405 is a diagram illustrating a lead
misplacement failure, where a lead 401 deviates from a pad 402. 406
is a projection waveform produced in this event when light cutting
line data detected within a processing window is projected in the
direction indicated in the figure. In 405, a solder fillet 403
attaches mostly to a side portion of the lead due to misplacement
of the lead, so that a lead portion cannot be easily distinguished
from a side fillet portion from the projection waveform 406.
In such a case, the image processing and tested-object shape
detecting means 11 may often detect a lead width including a side
fillet. However, since the failure occurring ratio is low in actual
manufacturing sites as mentioned above, an actual lead width can be
detected as a maximum peak of a histogram 407 when the histogram is
derived for detected lead widths for a complete board.
Likewise, when a lead width is estimated, lead misplacement may
frequently occurs if modifications in a manufacturing process
causes the process to be instable, whereby the largest detection
frequency does not always indicate the lead width. As described
above, since a lead misplacement causes the lead width to be
detected with a side fillet included therein, the lead width is
detected wider, but not narrower. Therefore, the narrowest one of
peaks in a histogram for detected lead widths may be designated as
the lead width.
A pad width can also be derived from the pad side edges detected by
the image processing and tested-object shape detecting means
111.
After estimating the shapes and dimensions of an object under
testing as described above, test parameters are updated in the test
parameter updating means 116. More specifically, described in the
test parameter storing means 110 are those previously inputted by
the user and those actually used in a test as a lead thickness, a
lead width, and a pad width of an object under testing. A lead
thickness, a lead width, and a pad width detected from images are
compared with respective values previously inputted by the user,
and when the values detected from the images are extremely
different from the values inputted by the user, the updating is not
performed as an error has taken place in the detection of the
shapes of the dimensions from the images.
Otherwise, the lead thickness, the lead width, and the pad width
detected from the images are stored as values to be actually used
for a test. For example, the image processing and tested-object
shape detecting means 111 digitizes the light cutting lines A 205
in FIG. 2 for detecting side edges of a lead as described above,
where a proper threshold value for this purpose may be the value
approximately one half of the lead thickness. Therefore, the value
of the lead thickness multiplied by 0.5 is stored as an image
processing parameter.
Also, since a design width and a design thickness of a lead are
required as defect determining parameters for determining defects
in the defect determining means 113 as mentioned above, the design
width and the design thickness of the lead (electrode) calculated
in the tested-object design dimension estimating means 115 are
stored as defect determining parameters, respectively, in the
defect determining means. Also, the values calculated in the
tested-object design dimension estimating means are used not only
as the defect determining parameters but also as image processing
parameters in the image processing and tested-object shape
detecting means through the test parameter storing means.
Next, an update timing for the test parameters will be described
with reference to FIG. 5. After an image is detected, the
processing of the image processing and tested-object shape
detecting means 111 and the defect detecting means 113 in FIG. 1 is
executed before detection of the next image is completed. This is
performed until all images of a complete printed circuit board have
been detected. After the image detection and the image processing
are completed, the dimension of an object under testing is
estimated in the tested-object design dimension estimating means
115 while the testing apparatus is loading a next printed circuit
board under testing, and subsequently test parameters are
updated.
While a method of estimating shapes and dimensions of an electrode
portion and a pad portion based only on the detection results of a
complete printed circuit board has been described with reference to
FIG. 5, some components mounted on a printed circuit board are
extremely few in number, in which case the histogram illustrated in
FIG. 3 or FIG. 4 cannot be satisfactorily calculated. In this case,
shapes and dimensions may be estimated based on the detection
results of electrode portions and pad portions detected from a
plurality of printed circuit boards. A timing chart for this is
illustrated in FIG. 6.
However, it is not necessary to accumulate the detection results of
electrodes of one type on a plurality of printed circuit boards,
when a large number of them are mounted on a single board. If this
were performed, a large accumulating region would be reserved in
the tested-object shape accumulating means 114 in FIG. 1. To
prevent this, detection results from a different number of printed
circuit boards may be used for each type of electrodes.
When the timing chart illustrated in FIG. 5 is used, a problem may
arise in that the test may be conducted using inaccurate dimensions
of an electrode (lead) and a pad for a printed circuit board which
is subjected to the test for the first time after the type of
component has been changed. FIG. 7 illustrates a timing chart for
preventing this. In FIG. 7, the processing of the image processing
and tested-object shape detecting means 111 is performed each time
an image is detected to derive the shape of an object under testing
and to accumulate the detection results, i.e., the positions of
side edges of a lead, the positions of side edges of a pad, and the
height of a top surface of the lead, in the tested-object shape
accumulating means. After this processing is performed for a whole
printed circuit board, characterizing amounts are estimated in the
tested-object design dimension estimating means 115 in FIG. 1, and
then defect determination is performed based on the shapes of
objects under testing on a complete printed circuit board, which
have been accumulated in the tested-object shape accumulating means
114, thereby making it possible to realize the defect determination
using accurate dimensions of the electrode and the ad.
While the previous description has been made on the assumption that
test parameters are updated after all images of a complete printed
circuit board have been detected, a large number of soldered
portions may be detected in a field of view of the image detector
104 in the exemplary configuration illustrated in FIG. 1, for
example, when a component comprises an extremely large number of
electrodes, for example, in the case of a 0.5 mm pitch QFP (quad
flat package). In this case, it is possible to estimate shapes and
dimensions of electrodes and pads in each field of view. A timing
chart for this approach is as illustrated in FIG. 8. An advantage
provided in this case is that an accumulating region can be reduced
in the tested-object shape accumulating means 114.
In the case where the model number of a mounted component is
previously known, or the like, a more reliable test may be realized
by again utilizing test parameters which were derived when a
component of the same model number was used before. Generally,
since the model number of a component is seldom changed many times
a day, the storage unit is adapted to be able to automatically
preserve the test parameters as backup for each day. By again
utilizing test parameters of a date when the same model number of
component was used, it is possible to omit a work for again
updating the test parameters based on test images.
While the test apparatus described in connection with FIG. 1
detects an image with an optical system composed of a TV camera and
a slit light projector to test components mounted on a printed
circuit board, the present scheme is effective with any method of
detecting a three-dimensional shape. For example, the present
approach is also applicable to a light section method which
combines a laser spot and PSD (position sensing detector), or the
like.
Also, the present invention may be applied to an apparatus which
detects an image with an optical system which does not detect a
three-dimensional shape, as illustrated in FIG. 9. 901, 902, 903
designate a printed circuit board, an electronic component under
testing, and an XY stage, respectively, which are similar to FIG.
1. 904 designates an image detector which detects an image of the
electronic component 902 illuminated by a ring illuminator 905. The
diameter of the ring illuminator 905 is set to be small such that a
bright-field illumination can be provided for 902.
906, 907 designate an image input means and a test parameter
storing means, respectively, which are similar to the image input
means 107 and the test parameter storing means 110 in FIG. 1. 908
designates an image processing means which detects the position of
a lead and the position of a pad. When the bright-field
illumination is performed, a lead and a pad, because of higher
reflectivities of their surfaces, are detected righter than
surrounding resist portions having a lower effectively. Stated
another way, this is an approach which detects the position of an
object under testing by a difference in brightness that is detected
based on the difference in reflectivity.
As illustrated in FIG. 10, a processing window 1004 is set above a
design position of the tip of a lead in the same figure. An image
within the processing window 1, 1004 is projected in the vertical
direction of the same figure to produce a brightness projection
waveform 1006, and edges are detected from this waveform to derive
the position of the lead.
Also, a processing window 2 is set below the design position of the
tip of the lead in the same figure so as not to include a solder
fillet. Similar processing to that for detecting the edges of the
lead is performed on an image within the processing window 2 to
detect the edges of a pad.
The defect determining means 909 derives the amount of misplacement
of the lead based on the lead edges and the pad edges detected by
the image processing means 908 as described above, and detects a
misplacement failure if the ratio of the amount of misplacement to
a design width of the lead is equal to or larger than a
predetermined threshold value.
910 designates a tested-object shape accumulating means which
records the positions of lead edges and ad edges detected in the
image processing means 908. 911 and 912 designate a tested-object
design dimension estimating means and a test parameter updating
means, respectively. While the tested-object design dimension
estimating means 115 in FIG. 1 estimates a lead thickness, a lead
width, and a pad width, the tested-object design dimension
estimating means 911 only estimates a lead width and a pad width.
An algorithm for estimating a lead width and a pad width used
herein may be similar to that of the tested-object design dimension
estimating means 115. The test parameter updating means 912
performs processing completely similar to the test parameter
updating means 116 to update the test parameters stored in the test
parameter storing means 907.
While in FIG. 1 and FIG. 9, design dimensions of a lead and a pad
are estimated in the tested-object design dimension estimating
means 115, 911, respectively, based on the shape of an object under
testing detected by the image processing means, it is also possible
to estimate standard values for characterizing amounts of a
soldered portion to perform a good/bad determination based on these
standard values for the characterizing amounts, without limited
only to the design dimensions.
FIG. 11 illustrates an explanatory diagram for the characterizing
amounts of a soldered portion. For determining whether a soldered
state is good or bad, a fillet height 1101 indicative of a maximum
height of a solder fillet in contact with a lead; a fillet length
1102 which is the length from the position of a lead toe to the tip
of the fillet; a fillet width 1103 at the position of the lead toe;
the volume of the fillet; an area of the fillet in contact with a
pad or the lead; and a wet angle 1104 of the fillet to the lead are
used as characterizing amounts.
As frequently used criteria for a non-defective unit, the fillet
height is equal to or higher than a height previously determined
for each type; the fillet width is in a predetermined proportion or
more to the width of a lead; the volume of the fillet and the
contact area with a pad or a lead are equal to or more than
predetermined threshold values; and the wet angle of the fillet to
the lead is equal to or more than a predetermined angle.
Incidentally, the fillet height is closely related to the wet
angle. Generally, when the fillet height is sufficiently high, the
wet angle is small in relation to surface tension, in which case a
lead and a pad are also favorably connected because of a large
amount of solder. Thus, when these two characterizing amounts are
combined to make up a determination item, a false result can be
reduced. Specifically, a failure is determined when the wet angle
is small and the fillet height is low, and a non-defective unit is
determined in other combinations.
Generally, the appearance of a soldered portion is visually tested.
Since it is difficult to strictly measure these characterizing
amounts, testing criteria are seldom determined strictly for the
characterizing amounts for a soldered portion.
In such a case, if the testing criteria can be automatically set
based on characterizing amounts detected by the apparatus, a time
for setting test parameters can be reduced. As mentioned above, the
failure occurring frequency in printed circuit boards is at most 1%
or less. For this reason, it is possible to identify that a portion
with a high occurring frequency in a histogram for detected values
of a characterizing amount of soldered portions calculated from a
large number of soldered portions under testing is a feature
indicating a non-defective unit.
Conversely, a portion of the histogram with a high occurring
frequency can be determined as a non-defective unit, while a
portion with a low occurring frequency as a defective unit. For
example, FIG. 12 illustrates a histogram for a solder fillet
length. Generally, a solder fillet is required to have a length
equal to or larger than a predetermined length. It is therefore
possible to classify a region with a low occurring frequency 1201
as a defective unit, a region with a high occurring frequency 1202
as a non-defective unit, and a region 1203 as a non-defective unit
since the fillet is not too short although the occurring frequency
is low.
Next, FIG. 13 illustrates an example of heights of fillets when
viewed from one side. 1301 designates solder fillets. When an image
of a top surface of a printed circuit board is detected by the
detection optical system illustrated in FIG. 1, a tilted top
surface of the printed circuit board may be detected due to bowing
of the printed circuit board. Since the top surface of the printed
circuit board locally includes differences in height due to the
presence and absence of resists and wiring patterns, it is
difficult to accurately detect a tilted top surface of a printed
circuit board. In such a case, the correlation between a fillet
height and a fillet position is linearly approximated as indicated
by 1302 using a least square method or the like, and a solder
fillet spaced from this approximation line by a large distance is
determined to be defective. Since the tilted top surface of the
printed circuit board is in parallel with the gradient of the
approximation line, it is possible to determine whether fillet a
height is good or bad without being influenced by bowing of printed
circuit boards.
As described above, while one of shape factors of a lead and a pad
and shape factors of solder fillets is used as a test parameter,
the solder testing apparatus is of course capable of accumulating
both shape factors so as to conduct a test based on one of the
shape factors. In addition, both shape factors may be accumulated
to conduct a fine test based on both the shape factors.
As described above, the present invention can produce an effect of
realizing a highly reliable test even when a plurality of model
numbers of electronic components having the same electric
characteristics are mounted as the same components by measuring
their shapes and dimensions based on detected images to set test
parameters.
* * * * *